High performance amplifier circuits using separate power supplies

Abstract

The present invention is an apparatus and method to provide a high supply rejection and a full rail-to-rail output swing in an amplifier circuit. A first stage generates a first output. The first stage is powered by a second supply. A second stage is coupled to the first stage to generate an amplifier output. The second stage is powered by a first supply. The first and second supplies are different in regulation mode. By making the second supply a low noise supply, the power supply noise amplified by the first stage is minimized, with the voltage gain of the second stage regaining the rail-to-rail swing lost by the first stage due to the regulator supplying very low noise power to the first stage.

What is claimed is:  
     
       1. An amplifier circuit comprising: 
       a first stage to receive an amplifier input and to generate a first output, the first stage being powered by a second supply and having a differential input;  
       a second stage coupled to the first stage to receive the first output and to generate an amplifier output, the second stage being powered by a first supply, the first and second supplies being different in regulation mode; and  
       a reference circuit, the reference circuit being powered by the second supply, one of the differential amplifier inputs being the output of the reference circuit.  
     
     
       2. The circuit of  claim 1 , wherein the first supply is an unregulated supply and the second supply is a regulated supply. 
     
     
       3. The circuit of  claim 1 , wherein the amplifier output has a rail-to-rail swing for the voltage range of the first supply. 
     
     
       4. The circuit of  claim 1 , wherein the second supply comprises a regulator powered by the first supply. 
     
     
       5. A method for providing high supply rejection and rail-to-rail output swing, the method comprising: 
       receiving an amplifier input by a first stage to generating a first output, the first stage being powered by a second supply and having a differential input;  
       generating an amplifier output by a second stage, the second stage receiving the first output, the second stage being powered by a first supply, the first and second supplies being different in regulation mode; and  
       coupling a reference voltage to one of the differential inputs of the first stage.  
     
     
       6. The method of  claim 5 , wherein the first supply is an unregulated supply and the second supply is a regulated supply. 
     
     
       7. The method of  claim 5 , wherein the amplifier output has a rail-to-rail swing for the voltage range of the first supply. 
     
     
       8. The method of  claim 5 , wherein the second supply comprises a regulator powered by the first supply. 
     
     
       9. An amplifier comprising, in an integrated circuit: 
       a regulator; and  
       a first stage and a second stage;  
       the first stage to receive an amplifier input and to generate a first output, the first stage having a differential input;  
       the second stage coupled to the first stage to receive the first output and to generate an amplifier output;  
       the second stage and the regulator being powered from a power supply coupled to terminals of the integrated circuit; and,  
       the first stage being powered by the regulator;  
       a reference circuit, the reference circuit being powered by the second supply, one of the differential amplifier inputs being the output of the reference circuit.  
     
     
       10. The integrated circuit of  claim 9 , wherein the amplifier output has a rail-to-rail swing for the voltage range of the power supply coupled to the integrated circuit terminals. 
     
     
       11. An amplifier comprising: 
       an integrated circuit having an inverting input including:  
       a voltage regulator providing power at a regulated voltage irrespective of voltage variations in power supplied to the voltage regulator; and  
       an amplifier having a first stage and a second stage;  
       the first stage to receive an amplifier input and to generate a first output;  
       the second stage coupled to the first stage to receive the first output and to generate an amplifier output;  
       the second stage and the regulator both being powered from a power supply coupled to terminals of the integrated circuit; and,  
       the first stage being powered by the regulator;  
       the amplifier further having a gain control feedback element coupled between the amplifier output and the inverting amplifier input.  
     
     
       12. The amplifier of  claim 11  wherein the feedback element is part of the integrated circuit. 
     
     
       13. The circuit of  claim 11 , wherein the amplifier output has a rail-to-rail swing for the voltage range of the power supply coupled to the terminals of the integrated circuit.